activateMenu = function(nav) {
  /* currentStyle restricts the Javascript to IE only */
  if (document.all &&
      document.getElementById(nav).currentStyle) {  
    var navroot = document.getElementById(nav);
          
    /* Get all the list items within the menu */
    var lis = navroot.getElementsByTagName("LI");  
    for (i=0; i<lis.length; i++) {    
      /* If the LI has another menu level */
      if(lis[i].lastChild.tagName=="UL") {              
        /* assign the function to the LI */
        lis[i].onmouseover=function() {	                  
          /* display the inner menu */
          this.lastChild.style.display = "block";
        }
        lis[i].onmouseout=function() {   
          this.lastChild.style.display = "none";
        }
      }
    }
  }
}

window.onload = function() {
  /* pass the function the id of the top level UL */
  /* remove one, when only using one menu */
  activateMenu("nav"); 
}